6-SFX (full name: 6-(Fluorescein-6-carboxamido)hexanoic acid, succinimidyl ester, single isomer) has a 6-atom aminohexanoyl spacer group that separates the fluorescein dye and the amine-reactive group. &lamba;Ex/&lamba;Em (pH 9) = 494/521 nm Yellow solid soluble in DMF, DMSO or pH>6.5 buffers Store at -20°C and protect from light C31H26N2O10 MW:586.55